Centrifugal delay switch



J. @a 94@ s, H, DlKE CENTRIFUGAL DELAY swnca Filed Feb. 20, 1943 Fi. i

20 32 v2l 28 28a 22 Z5 l 34 y l INVENR .3s/2% L6 Y Patented Jan. 4, 1949 CENTRIFUGAL DELAY SWITCH Sheldon H. Dike, Ventnor, N. J., assigner to the United States of America as represented by the Secretary of the Navy Application February 20, 1943, Serial No. 476,573

6 Claims. 1

This invention relates to safety switches for use in projectiles and more particularly to a novel safety switch actuated by a force present in the projectile during its ilight and which includes an electrical time delay means for controlling operation of the switch by the actuating force.

One object of the invention resides in the provision of a safety switch for projectiles which is closed when a predetermined period of time has elapsed after firing of the projectile. A switch made in accordance with the invention comprises a switch member movable between open circuit and closed circuit positions, preferably by centrifugal force, and a fusible element normally locking the switch member in one of its positions. The fusible element is adapted to be melted by heating means operable in response to a force of setback when the projectile is red, with the result that the switch member is released and moves to its operating position under centrifugal force. In the preferred construction, the switch member is movable in a cylinder, and the heating means is energized electrically by a circuit including the wall of the cylinder.

Another object of the invention is to provide in a projectile a centrifugally operable, time delay switch for preventing premature detonation of an explosive charge in the projectile.

A further object of the invention is to provide a novel time delay switch having means for establishing a positive electrical contact to arm a projectile detonating circuit.

Still another object of the invention is to provide a centrifugally operable. time delay switch characterized by its simplicity of construction and its high factor of safety in operation.

These and other objects of the invention may be better understood by reference to the accompanying drawing, in which Fig. 1 is a longitudinal sectional View of part of a projectile embodying one form of the new switch;

Fig. 2 is an enlarged, transverse sectional view of the switch shown in Fig. 1;

Fig. 3 is a sectional view on the line 3 3 in Fig. 2, and

Fig. 4 is a schematic view of the switch showing the electrical connections.

Referring to the drawing, I have shown the switch in agform suitable for use in an explosive projectile I of the type including a radio operated proximity fuze disposed in the nose portion. as disclosed in a co-pending application of M. A. Tuve et al., Serial No. 471,388, led January 6, 1943. More particularly, the projectile comprises a casing II and a cylindrical container or can I2 .threaded in the front end of the casing. The can extends rearwardly into the casing and is embedded in an explosive charge I3, the rear end of the can being closed. At its front end, the can is open and receives a. second can I4' to which the nose I5 of the projectile is secured, the cans I2 and I4 being connected together in any suitable manner. The nose I5 includes an antenna coupled to an oscillator unit I6 in the inner can I4, and the oscillator is electrically coupled to an amplifier unit Il in the rear end portion of the inner can.

The safety switch of my invention is mounted in a cylindrical housing I8, preferably made of insulating material, which fits closely in the outer can I2 to the rear of the inner can I Il and the amplier I'I. An electrical detonator (not shown) for exploding the charge I3 is disposed to the rear of the switch housing in the can I2, which may also contain the batteries for operating;r the amplier and oscillator units and supplying current to energize the detonator. The switch in housing I8, to be described in detail, is preferably included in the energizing circuit for the detonator and normally maintains the circuit open to prevent premature detonation due to accidental operation of the radio `apparatus or any other cause.

The switch housing I8 has a passage extendinc diametrically therethrough (Figs. 2 and 3i, the passagebeing enlarged at one end, as shown at 20, and having a reduced portion 2| intermediate its ends. A metal cylinder or sleeve 22 is disposed in the reduced portion 2l and terminates at its outer end in an enlarged end portion 23 of the passage which contains a pair of switch contacts 24 and 25. The contacts are preferably in the form of spaced metal pins extending transversely of the passage and embedded at their ends in the housing I8. The contact 25 is electrically connected to the sleeve 22, as by means of a conductor 26.

A heating element in the form of a carbon pellet 28 is slidably mounted in the sleeve 22 and carries at its outer end a. switch member 28a. On the opposite end of the pellet is a fusible element 23, which may be made of eutectic solder, and one end of a wire conductor 30 is embedded in the fusible element. The opposite end of the wire 30 is connected to a metal block 3I tted against the inner end of the enlarged portion 20 of the passage, the block being secured in the enlarged portion 20 by means of a pin 32 extending through the block and embedded at its ends in the housing I8. y

The contact 25 is electrically connected throug 3 a setback switch 34 and a wire 35 to the negative side of abattery 36 in the projectile, and the positive side of the .battery is connected through another setback switch 31 and a resistor 38 to the block 3|, the block having a suitable terminal (not shown) for connection to the resistor. The other contact 24 is connected through a wire 39 to one side of the electric detonator, the other side of which is connected through a wire 48 to the positive side of the battery between the setback switch 31 and the resistor 38.

The operation of the device is as follows: Normally, the switch is held open at the contacts 24-25 by the wire conductor 30 which locks the pellet 28 and switch member 28a at the inner end portion of sleeve 22. The Wire 30 has suiicient strength to prevent release of the switch member 28a and accidental closing of the switch due to handling of the projectile. When the projectile is red from a gun, the resulting force of setback closes the switches 34 and 31 with the result that the heating element 28 is energized through a circuit traceable from the positive side of the battery through switch 31, resistor 38, block 3|, wire 30, fusible element 29, the heater 28, sleeve 22, conductor 26, contact 25, switch 34, and wire 35 to the negative side of the battery. The heater 28 then commences to raise the temperature of the adjacent fusible element 29 until the latter reaches its fusing point, whereupon the end of the wire 30 embedded in the fusible element is released. The projectile I is rotated during its ilight, due to the action of the rifling in the gun barrel when the projectile is red, and since the heating pellet 28 is normally offset from the axis of rotation, the resulting centrifugal force moves the pellet and the switch member 28a outwardly in sleeve 22 on release of the wire 30, so that the switch member is wedged in the space between contacts 24 and 25. Accordingly, the contacts are bridged electrically by the switch member, and the detonating circuit including wires 39 and 4D is armed and ready to be energized upon operation of the radio apparatus.

The new switch is simple and compact in construction and contains relatively few moving parts. I have found that a time delay of between six and seven seconds can be obtained by the use of the fusible element 29, although by varying the consistency of the material of the fusible element the extent of the time delay may be varied. The carbon pellet 28 and the switch member 28a move as a unit under centrifugal force when they are released by the fusible element, and, therefore, the switch member has sufficient momentum to engage the pins 24 and 25 with considerable force so that it is wedged tightly between the pins and forms a proper electrical contact. The sleeve 22 serves not only as a cylinder in which the switch con- 4 tact 28a slides, but also as part of the electrical circuit for energizing the heating element 28 to release the switch.

I claim:

1. A switch comprising a switch member movable by centrifugal force between open-circuit and closed-circuit positions, a fusible el-ement normally locking the switch member in one of said positions, and means responsive to a force of setback for heating said element to release the switch member.

2. A safety switch for projectiles, which comprises a housing having a cylinder, a switch member movable in the cylinder between opencircuit and closed-circuit positions by centrifugal force, a fusible element normally locking the switch member in one of said positions, and a circuit including the wall of said cylinder for heating said element to release the switch member.

3. A safety switch for projectiles, which comprises a housing having a cylinder, a switch member movable in the cylinder between opencircuit and closed-circuit positions by centrifugal force, electrical heating means connected to the switch member, a fusible element connected to the heating means, a member embedded in said element for locking the switch member against movement, and a circuit including the locking member and the wall of said cylinder for energizing the heating means to fuze said element and release the switch member.

4. In an electric circuit, a switch member movable by centrifugal force between open-circuit and -closed-circuit positions, a fusible :element normally locking the switch member in one of said positions, an initially open switch closed under force of setback, and means in the circuit for heating said element to release the switch member.

5. In an electric control for an explosive projectile including an operating circuit having an initially open switch closed by setback, a safety circuit, a switch member movable under centrifugal force to open the safety circuit and close the operating circuit, and means for initially locking said member, said means being responsive to heat currents generated in the operating circuit for releasing the member.

6. In an electric control for an explosive projectile, a delay switch including a member movable by centrifugal force between open-circuit and closed-circuit positions, a heat responsive means initially locking said member in one of said positions, and means responsive to force of setback whereby the heat responsive locking means is released.

' SHELDON H. DIKE.

No references cited. 

